A phenolic compound is a compound produced by substituting a hydrogen atom on a benzene ring in an aromatic hydrocarbon with a hydroxyl, and may be divided into a monophenol and a polyphenol according the number of hydroxyls contained in its molecule. The phenolic wastewater is one of the industrial wastewater with large hazard and wide pollution range in the world today and is an important source of water pollution in the environment. In many industrial fields such as coal gas, coking, oil refining, metallurgy, machine manufacturing, glass, petrochemical engineering, wood fiber, chemical organic synthesis industry, plastic, medicine, pesticide and paint, the discharged wastewater contains the phenol. If the wastewater is not treated and is directly discharged to irrigate a farmland, the atmosphere, water, soil and food may be polluted. Along with the improvement of environmental protection requirements, the discharge standard of the phenolic wastewater is ever-increasing. With the phenolic wastewater, the discharge standard is required to be lower than 0.5 mg/L. The conventional organic wastewater treatment technologies (such as a physicochemical treatment technology, a biological treatment technology, wet oxidation and incineration) have the problems of high cost, low degradation rate, easily deviated secondary pollution and the like, and is difficult to meet the requirement of the wastewater treatment.
The supercritical water oxidation is a method with which organic matters are “combusted” and oxidized with air or other oxidants under a high temperature and high pressure condition of being beyond a critical point (PC=22.1 MPa, TC=374° C.) of water. The polarity of the water is a function of a temperature and a pressure and the supercritical water is a non-polar solvent. Under the environment of the supercritical water, the organic matters and the gas may be completely dissolved to each other, a phase interface between gas and liquid phases disappears, a homogeneous phase system is formed and thus the reaction speed is greatly accelerated. Within retention time that is less than 1 minute or even is several seconds, more than 99.9% of organic matters are quickly combusted and oxidized into CO2, H2O and other nontoxic and harmless final products. The reaction temperature is 400-650° C. generally, so the occurrence of secondary pollutants such as SO2, NOx, and dioxin is prevented. The supercritical water oxidation technology provides a guarantee for complete degradation and treatment of the phenolic wastewater.
At present, the corrosion and salt deposition are two technical problems to promote the supercritical water oxidation technology. The corrosion is mainly attributed to the formation of inorganic acids (such as HCl and H2SO4) in a supercritical water oxidation process and the reaction condition with a high temperature, a high pressure and a high oxygen concentration. Due to the nearly insoluble characteristic of inorganic salts in the supercritical water, a reactor and a pipeline are blocked. In addition, when materials pass through a heating component such as a heat exchange device or an electrical heater, the organic matters are easily pyrolyzed to produce coke, tar and the like. As the materials are pyrolyzed and coked at a preheating state, it is inevitable that the heat exchange efficiency of the heat exchange device and the electrical heater is greatly reduced. Generally, the wastewater contains the organic salts, which also occurs a salt deposition phenomenon at the preheating state. Because of a high temperature and high pressure reaction process, the materials need to be preheated and pressurized to a supercritical state, which results in the problems of high energy consumption and high cost.
A water membrane reactor is an effective method to comprehensively solve the problems of the corrosion and salt deposition. The reactor generally consists of a pressure-bearing outer shell and a porous inner shell. An organic waste liquid and an oxidant are injected from a top of the reactor to take place a supercritical water oxidative reaction, thus producing a high-temperature reaction fluid. The low-temperature evaporated water is injected into an annular space between the inner shell and the outer shell from a side of the reactor. The evaporated water may balance the pressure of the reaction fluid to the porous inner shell, so that the porous inner shell does not need to bear the pressure and the pressure-bearing outer shell is prevented from contacting the reaction fluid. The evaporated water is permeated into the reactor via the porous inner shell to form a layer of subcritical water membrane on a porous inner wall. The water membrane can prevent the contact between the inorganic acid and the wall and can dissolve the inorganic salts separated out in a supercritical temperature reaction area, so that the problems of the corrosion and salt deposition in the reactor can be effectively alleviated. Due to the flow field characteristic in the water membrane reactor and injection manner of the evaporated water, the evaporated water is distributed unevenly to cause local corrosion and salt deposition as well as the problem of local overheating (such as a nozzle and an upper portion of the reactor) in the reactor.